Factor VIII (FVIII) plays a critical role in the coagulation cascade by accelerating the conversion of factor X to factor Xa. Deficiency in FVIII activity is responsible for the bleeding disorder hemophilia A. The current treatment for hemophilia A is intravenous infusion of plasma-derived or recombinant FVIII protein. Despite this treatment being effective in controlling bleeding episodes, the requirement for frequent infusion, owing to the short half-life of FVIII (8-12 hours), makes it inherently costly. Gene therapy has emerged as an attractive strategy for the eventual cure of this disease. However, the progress in delivering FVIII gene using one of the most promising viral vectors, adeno-associated virus (AAV), has lagged behind the progress in delivering coagulation factor IX because of the large size of the FVIII coding sequence approaching the packaging capacity of AAV.
The present invention overcomes shortcomings in the art by providing a short synthetic liver-specific promoter and expression construct suitable for use in AAV vectors. The invention further provides FVIII proteins comprising additional glycosylation sites with amino acid sequence modifications and methods of their use in treating bleeding disorders.